The present invention relates to carboxylated styrenic resins and more particularly to an improved method for incorporating carboxyl functionality into preformed styrenic resins.
Hydrocarbon polymers such as polystyrene and the copolymers and graft polymers of styrene with acrylic esters, acrylonitriles and the like are generally incompatible or at best are only poorly compatible with dissimilar materials such as aliphatic and aromatic polyamides, widely termed nylon resins. Blends of certain nylon resins with some styrenic resins are known in the art, such as the blends of epsilon caprolactam polymers with acrylonitrile - styrene - butadiene (ABS) graft polymers exemplified in U.S. Pat. No. 3,134,746. Even though these known prior art blends exhibit many useful properties, lack of good compatibility between the polyamide and ABS often results in multi-phase or layered structures that exhibit poor interphase adhesion, with a concomitant tendency toward brittleness and delamination.
U.S. Pat. No. 3,668,274 discloses a method for preparing alloys of nylon resins and a multistage modifier resin consisting of a graft copolymer having an amine-reactive moiety copolymerized in the graft phase. The amine-reactive moiety, such as a copolymerizable carboxylic acid, is said to react with the amine end-groups of the nylon component to form covalent bonds between the nylon and graft copolymer components. These alloys are said not to exhibit phase separation during processing. More recently, in U.S. Pat. No. 4,496,690, the modification of styrenic resins to include an ethylenically-unsaturated carbonamide co-monomer is disclosed as reducing the tendency toward delamination in blends with nylons.
The presently available methods for combining styrenic resins and polyamides into alloys thus appear to be limited to use with specific styrenic copolymer resins or analogously modified polyamide resins. Preparing these specialty resins generally requires additional process steps, incurring increased costs and adding complexity to the manufacturing process. A method for the direct preparation of such alloys from commercially available, conventional styrenic resins and polyamides would greatly increase the number of resins that could be used in preparing such blends and lead to a wider variety of useful alloys. Such a process could be practiced either by the resin producer or by the resin compounder, and thus find wide application. Additionally, the over-all costs of producing such alloys could be reduced by eliminating the need for specialty styrenic resins, thereby benefiting the resin producer and the resin consumer.
Functional monomers have also been included in the preparation of styrenic resins where improved adhesion to mineral fillers is sought. Such added functionality may be useful to overcome the otherwise poor affinity of hydrocarbon resins for polar fillers such as glass fibers, clay fibers and the like. Without such modification, either by the surface treatment of the filler or by modification of the matrix resin, the resulting filled materials often exhibit reduced ductility and poor flexural strength.
A method for the direct incorporation of carboxylic functionality into commercially available, conventional preformed styrenic resins would be of substantial practical benefit to the resin industry. Such a process would greatly increase the variety of carboxylated styrenic resins available to the resin compounder for such applications as in preparing alloys of styrenic resins with polyamides, and for use in filled materials where such modification is needed to improve adhesion between the resin and the fillers.